reflect: add word-sized type intw that is int on most platforms, but uintptr on AVR platforms

Author: ydnar

src/reflect/intw.go

@@ -0,0 +1,8 @@
+//go:build !avr
+
+package reflect
+
+// intw is an integer type, used in places where an int is typically required,
+// except architectures where the size of an int != word size.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+type intw = int

src/reflect/intw_avr.go

@@ -0,0 +1,8 @@
+//go:build avr
+
+package reflect
+
+// intw is an integer type, used in places where an int is typically required,
+// except architectures where the size of an int != word size.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+type intw = uintptr

src/reflect/intw_avr_test.go

@@ -0,0 +1,23 @@
+//go:build avr
+
+package reflect_test
+
+import (
+	"reflect"
+	"testing"
+)
+
+// TestSliceHeaderIntegerSize verifies that SliceHeader.Len and Cap are type uintptr on AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestSliceHeaderIntegerSize(t *testing.T) {
+	var h reflect.SliceHeader
+	h.Len = uintptr(0)
+	h.Cap = uintptr(0)
+}
+
+// TestStringHeaderIntegerSize verifies that StringHeader.Len and Cap are type uintptr on AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestStringHeaderIntegerSize(t *testing.T) {
+	var h reflect.StringHeader
+	h.Len = uintptr(0)
+}

src/reflect/intw_test.go

@@ -0,0 +1,23 @@
+//go:build !avr
+
+package reflect_test
+
+import (
+	"reflect"
+	"testing"
+)
+
+// TestSliceHeaderIntegerSize verifies that SliceHeader.Len and Cap are type int on non-AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestSliceHeaderIntegerSize(t *testing.T) {
+	var h reflect.SliceHeader
+	h.Len = int(0)
+	h.Cap = int(0)
+}
+
+// TestStringHeaderIntegerSize verifies that StringHeader.Len and Cap are type int on non-AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestStringHeaderIntegerSize(t *testing.T) {
+	var h reflect.StringHeader
+	h.Len = int(0)
+}

src/reflect/value.go

@@ -1578,8 +1578,8 @@ type funcHeader struct {
 
 type SliceHeader struct {
 	Data uintptr
-	Len  uintptr
-	Cap  uintptr
+	Len  intw
+	Cap  intw
 }
 
 // Slice header that matches the underlying structure. Used for when we switch
@@ -1592,7 +1592,7 @@ type sliceHeader struct {
 
 type StringHeader struct {
 	Data uintptr
-	Len  uintptr
+	Len  intw
 }
 
 // Like sliceHeader, this type is used internally to make sure pointer and